Hello, I have a 1987 Ford Ranger. We just recently put in a different motor. It is a 2.9 liter V6. We put in a new thermostat, exhast system, spark plugs, wires, distributor cap, oil and filter. We have adjusted the timing and idle. We have done just about everything, but it is still getting poor gas mileage. What else could we do or check? The engine itself runs very smoth and doesnt have any flaws besides the fact that it doesnt have very much power and will only go 80MPH, and my old motor would do around 100MPH.

 

Welcome to FTE !

Thoughs/questions:

*Did it have a 2.9 before the engine swap?
*What is the current gas mileage and did you caculate it over maybe 3-5 tanks, filling it each and every time? Calculating mileage on one tankful is not a good indicator.
*Was timing set correctly? Some models require you to disconnect wiring or a jumper that impacts ignition timing before the timing is set. As we know, timing dramatically impacts performance and gas mileage.
*Was this a rebuilt or used engine? If used, how was the compression?

On edit: is the evap emission system functioning correctly?

 

O2 sensors can effect gas mileage.

 

Hello, and thanks for answering my post. The original engine before was the OEM motor. I was also a 2.9 liter. The engine that we put into it was the exact same thing, but it was from a 1988 ranger. It was also a 2.9 motor. I have calculated the gas mileage over 2 tanks now. I was getting about the same gas mileage from the previous engine, and it had a cracked head (reason for the swap). I get about 200 miles on a full tank. I am about 95% sure the truck has a 15 gallon tank. That would put me at about 13 MPG, and that seems about right for what I am getting from the truck. The timing was only off by about 1 point. There is a jumper that we did remove to check the timing. It was attached to the wiring harnes and had a cap that was pulled off to test it. The motor was not rebuilt. It was used from another truck, and it runs very well. We checked the compression while it was out and it was very good. As for the emission system, we never done anything with that, and I would not know what to do or where to begin. The only oxygen sensor that I know of was at the base of the Y pipe before the catalytic converters. That was broken off when we were reusing the Y pipe so it was replaced with a brand new one. Thanks again.

 

Do you have any indication of a rich condition, strong gas smell from the exhuast, black smoke, carbon build up in the exhaust pipe.

 

i have an 88 rangerthat has a new 2.9 rebuilt last year..the old factory motor had 260000 miles..and it got 20 mpg almost every tank since new!!...the rebuilt motor gets about 17 to 18. after 20000 ........i did find out that my front original cat is plugged up. maybe thats why the less mpg!

 

Well my truck does have two catalytic converters on it. We did put a new mufler and tailpipe on it, but we reused the catalytic converters and Y pipe when we put the different motor in. There is a good possibility that one (if not both) could be clogged. I don't recall exactly how many miles were on the new motor, but the old one (which was OEM) had around 150,000. I don't really believe that it is running on a rich mixture. The engine was running on "cold" mode for a while because the thermostat was bad. That was causing some problems with the engine registering with the computer when it is was warm enough to idle down. But that was all solved when we replaced the thermostat a few days ago and now the temperature has no problem. There is good flow of exhast out the tailpipe and nothing seems out of the ordinary with that.

 

You can put a vacuum gauge on the intake, bring it up to 2000-2500rpms for a few minutes, what the vacuum gauge, if it drops the cats MAY be clogged.